Full Idea
Four reasons for reducing everything to the categorical are: categorical predicates have wider scope; dispositions are variably realised by the categorical; categorical is 1st order, dispositions 2nd; categorical properties are explanatorily basic.
Gist of Idea
There are four reasons for seeing categorical properties as the most fundamental
Source
Stephen Mumford (Dispositions [1998], 08.5)
Book Reference
Mumford,Stephen: 'Dispositions' [OUP 1998], p.185
A Reaction
I particularly reject the fourth reason, as I take categorical properties as still in need of explanation. The categorical view is contingent (and Humean), but I take the categorical properties to be necessitated by the underlying powers.